The present invention relates generally to xe2x80x9cbubble trapxe2x80x9d devices that are used for removing gas bubbles from the extracorporeal circulation of blood.
Open heart surgery as well as other modern surgical procedures require that the patient""s blood be routed to an extracorporeal blood pump and oxygenator system. Extracorporeal support of blood perfusion provides many opportunities form air to be mixed with the circulating blood. Consequently it has become conventional practice to place a fine mesh filter called a xe2x80x9cbubble trapxe2x80x9d close to the blood return cannula. This device serves to trap gas bubbles before they are introduced into the body. This is an essential safety precaution as it is well known that gas bubbles can cause embolisms to form in the vasculature. Since the typical aortic return cannula commonly used in open heart surgery is located near the vessels that communicate with the brain, the possibility of a stroke from small bubbles is a distinct clinical concern. Recent evidence suggests that the presence of even very small micro bubbles is undesirable in perfusion procedures.
Bubbles having a diameter of just a few micrometers are impossible to remove using conventional filter technology. A porous mesh filter sufficiently small to xe2x80x9ctrapxe2x80x9d a small bubble has a very high flow resistance and this results in a very high-pressure differential across the mesh which is undesirable. For this reason among others there is a continuing need to improve bubble trap technology.
The bubble trap of the present invention is inserted into the external xe2x80x9cblood loopxe2x80x9d and blood is forced through the dynamic bubble trap by the blood pump. Typically the device is placed just ahead of the outlet cannula to act as a final-filter for the removal of bubbles just prior to the delivery of blood to the patient. The bubble trap device splits the blood flow into two streams. The first stream is fully bubble free and it is delivered to the patient. The secondary stream is smaller and it contains the micro bubbles removed from the in coming blood flow. This secondary flow is returned to the extracorporeal circuit upstream of the trap for additional degassing.
The blood flows through the bubble trap device from end to end and thus this flow is primarily axial in direction. Within the bubble trap device the blood flow is subjected to a strong radial acceleration so that there is a strong radial velocity imparted to the blood flow as well. A specialized helical separation chamber is used to impart this radial acceleration. The helix within the separation section comprises a center body and one or more blades. The design and the cross sectional areas of the separation zone are optimized to treat the blood cells gently while applying enough force to the small bubbles to concentrate them for removal.